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Blue Planet Live

In an exciting week of programmes, Blue Planet Live celebrated marine life and explores our oceans. 

About the programme

Blue Planet Live honours marine life from all corners of the globe as we dive deep to explore the health of our oceans. Gauging the state of our seas following key characters, from three different marine hotspots around the world in Mexico, Bahamas and on the Great Barrier Reef.

Read more about the series on the BBC's programme pages.

Discover the range of qualifications and modules from the OU related to this programme:

A Sea Turtle swims through the ocean, surrounded by fish

Copyright: BBC

A plastic bottle floating in the ocean

Monitoring and tackling plastic pollution

Plastics are ubiquitous in society, but poor disposal leads to widespread pollution especially in the rivers and oceans. How is this pollution monitored? How might we help tackle this pollution?

Plastic bottle pollution on the beach

Photo by Tim Hüfner on Unsplash

Plastics help keep our food and drink fresh, lightweight vehicles to save fuel, maintain sterile environments, and insulate buildings. So society uses an increasing amount of plastic materials each year and many of these are single-use or only used for a short lifetime. As a result this leads to a growing waste management challenge for society due to their low value.  The careless or poor disposal of plastic items means that many such items find their way into the natural environment and may then become widely dispersed. In particular plastics are frequently deposited in our rivers, oceans and coastal regions, as shown in the image to the right.

A key property that makes plastics suitable for many applications, in particular in packaging, is their ability to prevent the ingress of water and to be resistant to the attack of bacteria. Unfortunately these properties also lead to plastics being difficult to be broken down or degraded under many natural environmental conditions. Consequently if carelessly discarded in the environment plastics will last for a long time, (as shown below) and begin to accumulate.

Plastic pollution in the rivers and oceans

3:00 min

Copyright: BBC

It should be remembered that as members of society we can all have an influence on plastic pollution in the products we buy, how we use them and how we dispose of them.

As an introduction to plastic pollution and how it is monitored watch the video below. In particular note the discussion on plastics at the end of their life, their appearance and the sizes of those that are collected.

  • In the video, why are there growing concerns about the smaller plastic particles?
  • These can become trapped and retained. They may also act as a vector to transport chemicals to the creatures that ingest them. This affects both creatures in the seas, beaches and consequently may influence our food chain.

The term microplastics has been coined for plastic fragments that have dimensions smaller than 5mm and many of these were seen in the previous video. Due to their small size many marine species can ingest microplastics, even such small creatures as zooplankton (Botterell et al., 2019) upon which other sea creatures feed. This provides a pathway into our food chain, for instance plastic debris has been found in fish and shellfish (Rochman et al, 2015).  It is noteworthy that this same study also found fibres from synthetic (i.e. plastic) textiles in some fish samples from the USA. Such fibres may well have originated from laundry and passed through wastewater treatment plants, which members of the public may not have considered as a source of plastic pollution. Furthermore researchers have demonstrated that performing laundry can produce a large number of microfibers in the wastewater (Hartline et al., 2016).

How long until it's gone? Decomposition rates for common marine debris

Copyright: NOAA

It is clear from our discussion so far that plastic pollution is a significant challenge and one that scientists are continuing to research. However scientists, engineers and technologists are also researching ways to tackle plastic pollution by developing more environmentally friendly plastics. For instance a recent study compared the degradation of several biodegradable polyesters in both freshwater and seawater finding that only one example showed 100% degradation under the test conditions after 1 year (Bagheri et al., 2017). This highlights that it is a complicated issue for society though, as some of the biodegradable polyesters tested would degrade if composted under appropriate industrial composting conditions due to the elevated temperatures and the presence of a greater number of bacteria.

Starch film derives from a natural polymer and is increasingly being modified for use in plastic packaging applications. However again it should be disposed of in an appropriate manner, particularly as starch based bioplastic carrier bags were shown to degrade in soil or compost but were very slow to degrade in seawater (Accinelli et al., 2012).

It should be remembered that as members of society we can all have an influence on plastic pollution in the products we buy, how we use them and how we dispose of them. Notably we are all able to adopt a responsible approach and so try to better satisfy the 3Rs of reduce, reuse and recycle where plastics are concerned especially around the issues of littering and pollution in our rivers and oceans.

A pair of kobudai fish confront each other, mouth-to-mouth

Why do some fish change sex?

The Kobudai is a hermaphroditic species, meaning it can change sex. Why? Miranda Dyson explains the biological process...

In the first episode of Blue Planet II we met the Kobudai – the Asian sheepshead wrasse - that was introduced as a female, behaved like a female and looked like a female. And then, as we watched she slowly but surely morphed into a male – displayed male behaviours and developed male characteristics. It may seem strange but in fact it's common among fish. Known as sequential hermaphrodism, sex change is a common and usual adaptive part of the life cycle. It is documented in at least 27 families of fish, spread across nine orders and displays three patterns: changing from female to male, known as protogyny; changing from male to female, known as protandry; and serial bidirectional sex change. All three types of sex change occurs across the teleost tree of life, which suggest that it has evolved multiple times – but why?

gender symbols male and female

The biological processes and adaptive advantages of sex change has fascinated scientists for decades and the ecological and evolutionary contexts in which it occurs is now quite well studied and understood. The dominant theory as to why it occurs is known as the size advantage model. According to this model, changing sex is adaptive if your reproductive value (the number of offspring you can produce) is greater when you are a female when small, but a male when you are older and hence larger (as in the Kobudai) or vice versa. So by changing sex, lifetime reproductive success is maximized (the combined number of offspring you produce as a female and then a male or the other way round). Whether or not a species in protandrous or protogynous depends on their mating system and social structure. Protogyny – changing from a female to a male – is more common in fish than protandry because many fish have a mating system where large males, because of their superior competitive ability (in fights and contests with smaller males), are able to monopolize females and prevent smaller males from mating with them. Under these circumstances, reproducing initially as a female when small and then changing sex and becoming a male when large is the best strategy in order to maximize the number of offspring you leave in the next generation.

...more sneaker males occur in groups where the density of fish is high and the ability of dominant males to monopolize females is reduced.

Female to male change is common in the social wrasses like the blue headed wrasse and the Kobedai (though little is known about this species). The mating system is such that, large dominant males defend spawning sites which females need to lay their eggs so only males that are big enough to defend these sites are likely to mate.  The best option her then, is to be a female when you are small and once you grow large enough, change into a male.  In the blue headed wrasse, loss of the dominant male stimulates sex change in the largest female (typically) of the social group and involves dramatic changes in behaviour, anatomy and colouration.

Most juvenile blue headed wrasses develop as females but a few develop into small female-mimic males. These males are known as sneaker males, which try and sneak matings with females without the dominant male realizing. The number of fish that develop into sneaker males is also dependent on the social structure of the group – more sneaker males occur in groups where the density of fish is high and the ability of dominant males to monopolize females is reduced. A recent study suggests that in the Kobudai there are no sneaker males – males are derived directly from females.

A picture of a purple and green coloured Gobiodon histrio fish resting among some underwater coral

Dr. Oliver SchneiderCC BY-SA 3.0, via Wikimedia Commons

In species that change from male to female, the mating system in different usually consisting of monogamous pairs (where males and females pair during the breeding season and stay together and the male usually helps in looking after eggs) or where mating is random with respect to size. So, in these species male size doesn’t influence whether or not you mate with a female. But, larger females produce many more eggs than small females so it is adaptive to change to a female when large. For example, some species of anemone fish (one of which you will meet in the episode “Coasts”) live in small groups consisting of a small male and a dominant female plus smaller subordinate non-breeding individuals. The loss of the dominant female prompts the male to change sex and become the dominant female and one of the immature fish to become the new breeding male.

Fish that change back and forth between sexes is much rarer but is the strategy adopted by some species of coral gobi. It is not easily explained by the size advantage model however.  Current thinking is that coral gobis experience limited mating opportunities because they live in specialized niches and seldom move between isolated colonies of coral due to predation risk. The ability to change sex in either direction makes it easier for any two fish to form a pair without moving and also reduces the time between breeding events.

How does sex change occur?

This transformation can occur rapidly, in the blue-headed wrasse taking as little as 8 days

In many sequential hermaphrodite fishes, tissues of both sexes are present in the gonad prior to sex change whereas in others reproductive tissues are completely replaced by the secondary sex. In wrasses, complete restructuring of reproductive tissues occurs because no testicular tissue is present in the ovary prior to sex change. This transformation can occur rapidly, in the blue-headed wrasse taking as little as 8 days.  Sexual differentiation and gonadal development in fish depends on the balance between oestrogen (female hormone) and androgen (male hormone) production. In sex changing fishes, dramatic shifts in sex hormones accompany gonadal sex change but what tips the balance towards male or female steroid production remains unclear.

If you would like to learn more about the adaptive reproductive strategies employed by animals to maximize mating success as well  as the evolutionary implications you may consider studying S295 The biology of survival and S317 Biological Science: from genes to species.

Meet the experts

Professor of Environmental Health
Professor Toni GladdingProfessor of Environmental Health - School of Engineering & InnovationVIEW FULL PROFILE
Professor of Environmental Health
Professor Toni GladdingProfessor of Environmental Health - School of Engineering & Innovation

Toni has been involved in the waste management industry since 1992, and has researched the environmental and occupational impacts of waste management throughout this time. She has had funding from the Environment Agency, Defra, NERC and Zero Waste Scotland to research issues including waste collection frequency, air quality around waste plants, emissions, environmental impacts of recycling facilities and the health issues associated with waste management.

Dr Miranda DysonSenior Lecturer in Biology - School of Environment, Earth & Ecosystem SciencesVIEW FULL PROFILE
Dr Miranda DysonSenior Lecturer in Biology - School of Environment, Earth & Ecosystem Sciences

I am a Behavioural Ecologist and my primary interest lies with animal communication and sexual selection. Much of my research has focused on vocal communication with an emphasis on behavioural investigations of intraspecific female mate choice in anuran amphibians.

 I also have an interest in  fiddler crab reproductive behaviour and mate choice, the mating behaviour and male parental care in giant water bugs and duetting in birds. My current research interests include the relationship between bumblebees and snakeshead fritillaries on floodplain meadows. 

Dr Carl BoardmanLecturer - Energy & Environmental Sciences, Science, Technology, Engineering and MathsVIEW FULL PROFILE
Dr Carl BoardmanLecturer - Energy & Environmental Sciences, Science, Technology, Engineering and Maths

I’m an interdisciplinary research scientist that looks at the environmental impact of waste management processes and end-of-life materials. 

My main focus is on understanding how plastic products breakdown within different environments (e.g. composting, anaerobic digestion, terrestrial soils and the world’s oceans) and the impact their presence may have on the microbiology of the oceans and health of animals. 

My specific expertise in this area however is understanding the speed at which carbon materials breakdown and investigating what the controlling variables are. Other research interests include quantifying greenhouse gas emission from natural ecosystem and using satellite technology to investigate natural global phenomenon (e.g. pollution in the oceans and deforestation).  

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